A physicist has calculated another effect of general relativity on Mercury’s orbit.

It would take approximately two billion years to add one degree of Mercury’s orbit’s rotation.

These calculations will be verified by the Japan and European Space agency in their next mission to Mercury, which is expected to launch in October 2018.

Mercury revolves around the Sun in an unusual orbit, which is more elliptical as compared to other planets. Before Albert Einstein gave his general theory of relativity, astronomers’ predictions for Mercury’s orbit was not that accurate.

However, when Einstein realized that the theory accounted for the mismatch, it was the first evidence his general relativity was correct. It gave the right answer to explain the Mercury’s orbit. Recently, the math related to Mercury’s orbit has been slightly altered (for a 2nd time).

Clifford Martin Will, mathematical physicist, has computed another effect of Einstein general relativity on Mercury’s orbit. The effect hasn’t been detected so far because it’s too small.

What He Has Detected?

All planets in our solar system have elliptical orbits, which moderately rotate as each planet revolves around the Sun. Gravitational pulls from the other planets are responsible for this rotation. However, Einstein’s theory says that gravity comes from giant bodies like planets and the Sun warping spacetime.

The rotation of each planet’s orbit is affected by the warping caused by the Sun. This effect is almost null, but since the mercury is closed to the Sun, its effect would be notable.

The warping caused by the Sun (spacetime distortion caused by massive objects) also changes how rest of the planets in solar system pull on Mercury. Similarly, warping of the planets alters Sun’s pull on Mercury. The overall impact is too low; to add one degree of Mercury’s orbit’s rotation, it would take approximately two billion years.

Spacetime distortion | NASA’s Goddard Space Flight Center

Technical Details

Clifford Will point out a new factor in general relativity that contributes to Mercury’s perihelion advance (point in the orbit at which planet is closest to Sun). It’s much smaller than impacts produced from solar angular momentum and quadrupole moment, but hundred times bigger than the impact caused by second-post-Newtonian (20th-century Newtonian dynamics).

The new impact is a part of post-Newtonian equations that occurs because of the interaction between Mercury and the Sun, and between Mercury and the other planets. It also considers the interaction between motion of Mercury and other planets’ gravitomagnetic field.

Mercury Orbit

More specifically, the impact of inertial frames caused by the solar angular momentum is at the parts in hundred thousand level, while the newly detected impacts are at parts in million. Furthermore, the impact due to Newtonian dynamics is far less; at parts in ten million.
The new calculations (few parts in million) suggest a general relativistic precession of 42.98 arcseconds per 100 years.

Researchers will soon verify the calculations done by Clifford Will. The Japan Aerospace Exploration Agency and the European Space Agency are working on a joint mission, named BepiColombo, to the planet Mercury.

It will perform a comprehensive study of Mercury, including its surface, interior structure, magnetosphere and magnetic field. The mission is set to launch in October 2018, and it will enter the Mercury orbit in December 2025.